1. Field of the Invention
The present invention relates to a liquid ejection apparatus and a liquid supply method based on a “pit-stop” supply system in which a main tank and a sub tank are provided, and the main tank and the sub tank are connected together when it is necessary to supply ink from the main tank to the sub tank.
2. Description of the Related Art
Japanese Patent Application Publication No. 2006-35850 describes an apparatus in which, in order to achieve high-speed supply of ink during a pit-stop supply operation, a leaf spring made of a shape memory alloy is provided inside a sub tank to form a negative pressure generating device, and by passing current through the leaf spring and heating same during a pit-stop supply operation, the spring constant is raised two-fold, thereby causing the negative pressure during supply of liquid to become greater than the negative pressure at other times.
Japanese Patent Application Publication No. 2000-141687 discloses an apparatus comprising, provided with an ink supply channel, a hermetically sealed ink bag, a case which covers and hermetically seals the ink bag, a pressure adjusting device which is capable of adjusting the pressure of the air between the ink bag and the case, a first opening and closing valve provided at the ink inlet of the ink bag, and a second opening and closing valve provided at the ink outlet. Ink is supplied to the ink bag and the negative pressure thereof is adjusted by closing the second opening and closing valve, opening the first opening and closing valve, and adjusting the pressure between the ink bag and the case. Furthermore, after supplying ink to the ink bag, the first opening and closing valve is closed, the pressure between the ink bag and the case is maintained, and the second opening and closing valve is opened.
If using a shape memory alloy as described in Japanese Patent Application Publication No. 2006-35850, after supplying ink by heating the alloy, a long time is required until the temperature of the shape memory alloy falls and the pressure inside the sub tank returns to a suitable negative pressure for printing. If liquid is ejected from the liquid ejection head immediately after the supply of ink, then since the pressure in the sub tank is greater than the suitable negative pressure for printing, immediately after the supply of ink, the droplets of liquid ejected from the liquid ejection head become smaller in size. Furthermore, if using a shape memory alloy, in general, it is only possible to raise the spring constant by approximately two times. In other words, it is only possible to increase the ink supply speed by approximately two times.
In a system which utilizes the air pressure between an ink bag and a case in order to supply ink, as described in Japanese Patent Application Publication No. 2000-141687, since the air is compressible, then it is not possible to supply ink at high speed. Furthermore, if ink is supplied by adjusting the internal pressure of the sub tank to a pressure in the region of the negative pressure specified for printing, then the ink supply speed becomes slower.